Method of making metallic magnesium



Patented June 14, 1932 UNITED STATES PATENT OFFICE- SHELDON B. HEATH, OI! MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, -A CORPORATION OF MICHIGAN METHOD O1 MAKING METALLIC MAGNESIUM No Drawing.

The present invention concerns a method of producing metallic magnesium by the electrolysis of a fused bath containing magnesium chloride (MgCl and concerns more particularly the method of maintaining the bath by feeding to it a compound of magnesium. y l

In the electrolysis of such a fused bath wherein metallic magnesium is liberated and collects at the cathode and chlorine is liber ated'and drawn off at the anode, continuous operation isdesirable and it becomes necessary to replenish the bath and maintain it of the desired character by feeding thereto an equivalent of the magnesium and chlorine or other essential ingredients which, in the course of operation, have been or may be removed ther'efromL It is well known that the ideal feed to such a cell comprises anhydrous MgCl andthat accompanying water will reduce the current and power efficiency of electrolysis. It is further known that inert constituents of the feed, such as MgO, tend to settle out of the bath, and unless removed therefrom, will accumulate and interfere with continuous operation. jSuch sediment must accordingly be removed, which is customarily done by dipping from time to time as required, but this operation removes "also part of the bath along with the sediment or so-called sludge. In

I practice I have found that as high as two equivalents of MgCl may be removed in that way with one equivalent of sludge figured as 'MgO. The bath so removed with the sludge must, of course, be returned by feeding to the cell the constituents removed in addition to that required to replenish the MgCl converted to metal and chlorine.

, Anhydrous MgCl is not only diflicult and expensive to prepare, buton account of its hygroscopic properties it is practically impossible to handle it without its taking up some'moisture, and in practice, a content of Application filed May 25, 1928. Serial No. 280,659.

I have discovered an improved method of introducing the MgCl fed to such an electrolytic cell, having advantages as contrasted with the method therein disclosed, said improved method of feeding involving broadly the introduction of MgCl containing basic salt,- such, as magnesium wiry-chloride (MgOHGl).

To the accomplishment of the foregoing and related ends, the invention, then, consists' of the steps hereinafter fully described and particularly pointed out in the claim, the following description setting forth in detail one approved method of carrying out my invention, 1

I have found that when MgCl containing water is introduced into a fused bath containing MgCl such as may be used in an electrolytic cell for the production of metallic magnesium and chlorine, decomposition occurs consuming the heat of the cell and bath to form gaseous products containing HCl and basic salt corresponding to a portion of the accompanying water. Such basic salt I find corresponds to the oXy-chloride (MgOHCl).

I have found that instead of feeding such MgCl containing water it is more advantageous to further dehydrate with cheaper heat than that available in an electrolytic cell to formMgCl containing a portion of the basic salt corresponding to MgOI-ICl and to feed that product to the cell as the source of MgCl therefor. Such a product enters into the bath without decomposition.

, In the patent cited above there is disclosed and claimed the'method of feeding magnesium chloride adjacent the anode, but I have found that magnesium chloride containing small quantities of basic salt may be fed adjacent the cathode or through the new tralzone if the cell be of a type providing such a zone. 'I have found that MgCl con taining as high as 5% equivalent MgOHCl may be fed to either anode or cathode or neutral zone. If the content of basic chloride be in excess of 5% I prefer, however, to feed it adjacent the anode.

Magnesium chloride prepared as MgCl anhydrous containing a small amount of basic chloride is an intermediate product in the preparation of a' strictly anhydrous chloride according to certain methods of procedure and is therefore a cheapersource of magnesium than is the still further processed anhydrous,

anhydrous material.

When hydrated magnesium chloride is dried, either in air, wet or dry, or in any inert atmosphere, whether at reduced-pressure or in vacuum until all wateras such together with hydrochloric acid is driven off, there results a product containing magnesium, chlorine, oxygen and hydrogen. A peculiarity of this product is that if the hydrogen content befigured as water (H 0) and the remaining oxygen be figured as magnesium oxide MgO the molecular ratio of the latter to the former is constant at unity, no matter what the total content of such hydrogen and oxygen'may be, it being understood that such total content will vary depending upon the method and rate of drying. This it is believed indicates that the. product in question is comprised of magnesium chloride (MgCl and the oxychloride (MgOHCl) For want of a better term, this product is hence referred to as magnesium chloride containing basic magnesium chloride; however, it is not intended thereby to define the product to one having any precise constitutional ent of the bath such as NaGl or NaF may be formula.

If desired, the aforesaid product may be fed to the cell in inolten condition, and thereby conserve the heat of the cell. 7

It should be noted further that, in practice, other additive constituents or constltudesirably used, and .such will be removed alongwith the magnesium constituent with the dipped sludge. Depletion of such constituents or constituent if so or otherwise removed will necessarlly require a correspondmg amount to be added to maintain the bath of the desired composition and such addition may convenient y be made along with the feed of the magnesium salt used.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as re aids the method herein disclosed, provide the step or steps stated b the following claim or the equivalent of sue statedstep or steps be em loyed. I therefore particularly point out and distinctly claim as my invention In a method-of producing metallic magnesium, includingthe electrolysis of a fused bath containing magnesium chloride, the step which consists in maintaining said bath by introducing adjacent the anode magnesium chloride containing in excess of five per cent.

of basic magnesium chloride. Signed by me this 14 day of'Ma 1928,

' SHELDON B. 

